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https://issues.apache.org/jira/browse/SPARK-14277?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15218939#comment-15218939
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Apache Spark commented on SPARK-14277:
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User 'sitalkedia' has created a pull request for this issue:
https://github.com/apache/spark/pull/12074
> UnsafeSorterSpillReader should do buffered read from underlying compression
> stream
> ----------------------------------------------------------------------------------
>
> Key: SPARK-14277
> URL: https://issues.apache.org/jira/browse/SPARK-14277
> Project: Spark
> Issue Type: Improvement
> Components: Shuffle
> Affects Versions: 1.6.1
> Reporter: Sital Kedia
>
> While running a Spark job which is spilling a lot of data in reduce phase, we
> see that significant amount of CPU is being consumed in native Snappy
> ArrayCopy method (Please see the stack trace below).
> Stack trace -
> org.xerial.snappy.SnappyNative.$$YJP$$arrayCopy(Native Method)
> org.xerial.snappy.SnappyNative.arrayCopy(SnappyNative.java)
> org.xerial.snappy.Snappy.arrayCopy(Snappy.java:85)
> org.xerial.snappy.SnappyInputStream.rawRead(SnappyInputStream.java:190)
> org.xerial.snappy.SnappyInputStream.read(SnappyInputStream.java:163)
> java.io.DataInputStream.readFully(DataInputStream.java:195)
> java.io.DataInputStream.readLong(DataInputStream.java:416)
> org.apache.spark.util.collection.unsafe.sort.UnsafeSorterSpillReader.loadNext(UnsafeSorterSpillReader.java:71)
> org.apache.spark.util.collection.unsafe.sort.UnsafeSorterSpillMerger$2.loadNext(UnsafeSorterSpillMerger.java:79)
> org.apache.spark.sql.execution.UnsafeExternalRowSorter$1.next(UnsafeExternalRowSorter.java:136)
> org.apache.spark.sql.execution.UnsafeExternalRowSorter$1.next(UnsafeExternalRowSorter.java:123)
> The reason for that is the SpillReader does a lot of small reads from the
> underlying snappy compressed stream and we pay a heavy cost of jni calls for
> these small reads. The SpillReader should instead do a buffered read from the
> underlying snappy compressed stream.
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